Data storage device sorting access commands based on peak current for multiple actuators

ABSTRACT

A data storage device comprising a first actuator configured to actuate a first head over a first disk surface, and a second actuator configured to actuate a second head over a second disk surface. A plurality of access commands are received from a host, and a cost metric is computed for executing a seek to execute each access command of the plurality of access commands, wherein the cost metric is based on an access latency of the seek, a power consumption of the seek, and an estimated combined current draw of the first and second actuators during the seek. The access commands are sorted into an execution order based on the cost metrics computed for the access commands.

BACKGROUND

Data storage devices such as disk drives comprise a disk and a headconnected to a distal end of an actuator arm which is rotated about apivot by a voice coil motor (VCM) to position the head radially over thedisk. The disk comprises a plurality of radially spaced, concentrictracks for recording user data sectors and embedded servo sectors. Theembedded servo sectors comprise head positioning information (e.g., atrack address) which is read by the head and processed by a servocontroller to control the velocity of the actuator arm as it seeks fromtrack to track.

A disk drive typically comprises a plurality of disks each having a topand bottom surface accessed by a respective head. That is, the VCMtypically rotates a number of actuator arms about a pivot in order tosimultaneously position a number of heads over respective disk surfacesbased on servo data recorded on each disk surface. FIG. 1 shows a priorart disk format 2 as comprising a number of servo tracks 4 defined byservo sectors 6 ₀-6 _(N) recorded around the circumference of each servotrack. Each servo sector 6 _(i) comprises a preamble 8 for storing aperiodic pattern, which allows proper gain adjustment and timingsynchronization of the read signal, and a sync mark 10 for storing aspecial pattern used to symbol synchronize to a servo data field 12. Theservo data field 12 stores coarse head positioning information, such asa servo track address, used to position the head over a target datatrack during a seek operation. Each servo sector 6 _(i) furthercomprises groups of servo bursts 14 (e.g., N and Q servo bursts), whichare recorded with a predetermined phase relative to one another andrelative to the servo track centerlines. The phase based servo bursts 14provide fine head position information used for centerline trackingwhile accessing a data track during write/read operations. A positionerror signal (PES) is generated by reading the servo bursts 14, whereinthe PES represents a measured position of the head relative to acenterline of a target servo track. A servo controller processes the PESto generate a control signal applied to a head actuator (e.g., a voicecoil motor) in order to actuate the head radially over the disk in adirection that reduces the PES.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servotracks defined by servo sectors.

FIGS. 2A and 2B show a data storage device in the form of a disk driveaccording to an embodiment comprising multiple actuators configured toconcurrently actuate heads over respective disk surfaces.

FIG. 2C is a flow diagram according to an embodiment wherein accesscommands are sorted into an execution order based on a cost metric ofeach corresponding seek computed from an access latency, a powerconsumption, and an estimated combined current draw from multipleactuators.

FIG. 3A shows an embodiment wherein a command queue is maintained foreach actuator.

FIGS. 3B and 3C show an embodiment wherein an execution order for eachactuator results in a concurrent seek of at least two actuators.

FIGS. 4A and 4B show an embodiment wherein an acceleration current ofthe second actuator is decreased during an acceleration phase in orderto avoid an overcurrent condition during a concurrent seek.

FIGS. 5A and 5B show an embodiment wherein an acceleration phase of thesecond actuator is delayed in order to avoid an overcurrent conditionduring a concurrent seek.

FIGS. 6A and 6B show an embodiment wherein an acceleration current ofthe second actuator is increased and a deceleration phase is executedearlier in order to avoid an overcurrent condition during a concurrentseek.

FIGS. 7A and 7B show an embodiment wherein a peak current window isestimated for each actuator relative to a seek length, wherein the peakcurrent windows are evaluated to predict an overcurrent condition duringa concurrent seek.

FIG. 8 is a flow diagram according to an embodiment wherein the accesscommands are first sorted into a plurality of candidate execution ordersindependent of the combined current draw of the actuators, and then anexecution order is selected from the candidates based on the estimatedcombined current draw.

FIGS. 9A and 9B show an embodiment wherein the access commands of twoactuators are first sorted into two candidate execution orders, and thenan execution order is selected from the candidates based on theestimated combined current draw of the actuators.

DETAILED DESCRIPTION

FIGS. 2A and 2B show a data storage device in the form of a disk driveaccording to an embodiment comprising a first actuator 16 ₁ configuredto actuate a first head 181 over a first disk surface 201, and a secondactuator 16 ₂ configured to actuate a second head 182 over a second disksurface 202. The disk drive further comprises control circuitry 22configured to execute the flow diagram of FIG. 2C, wherein a pluralityof access commands are received from a host (block 24), and a costmetric is computed for executing a seek to execute each access commandof the plurality of access commands, wherein the cost metric is based onan access latency of the seek, a power consumption of the seek, and anestimated combined current draw of the first and second actuators duringthe seek (block 26). The access commands are sorted into an executionorder based on the cost metrics computed for the access commands (block28).

Any suitable actuators may be employed to seek the heads over respectivedisk surfaces, wherein in the embodiment of FIG. 2A a first voice coilmotor (VCM) 16 ₁ rotates a first set of actuator arms about a pivot, anda second VCM 16 ₂ rotates a second set of actuator arms about the pivotin a configuration referred to as a dual actuator. In other embodiments,each VCM may rotate respective actuator arms about independent pivots(e.g., first and second VCMs mounted at opposite sides of the disks). Inaddition, each head may be actuated by any suitable secondary actuator,such as a secondary actuator configured to actuate a suspension relativeto the actuator arm, and/or a secondary actuator configured to actuatethe head relative to the suspension.

In one embodiment, the amount of current the disk drive may draw from asupply voltage may be limited due, for example, to a current limit of apower supply that is powering the disk drive. When the current limit isexceeded, it may cause a supply voltage to fall below an emergencythreshold causing an emergency power-fail procedure to retract the headsfrom the disks before the air bearing dissipates. When the seek profilesof the multiple actuators overlap, and particularly when theacceleration or deceleration phase of the seek profiles overlap, thecombined current draw of both actuators may cause an overcurrentcondition. Accordingly in one embodiment when sorting the accesscommands into an execution order, an estimated combined current draw ofthe actuators is included in the cost metric of the sorting algorithm inorder to avoid the overcurrent condition.

FIGS. 3A-3B show an embodiment wherein the control circuitry 22maintains a command queue for each VCM, wherein the access commands ofeach command queue are sorted into an execution order based on asuitable cost metric associated with seeking the heads. Conventionally,the cost metric included different performance aspects such as theaccess latency or power consumption of a seek. That is, the sortingalgorithm may sort the access commands in a command queue in an orderthat minimizes the accumulated cost metrics using a suitable searchtree. In the example of FIG. 3A, the command queue stores three pendingcommands together with the current command being executed. FIG. 3B showsa corresponding tree search for the first VCM 16 ₁, and FIG. 3C shows acorresponding search tree for the second VCM 16 ₂. Each branch of thesearch tree has an associated cost metric, wherein the cost metric isaccumulated for each possible path through the search tree. The pendingcommands in the command queue are sorted into an execution order basedon the path through the search tree having the smallest accumulated costmetric.

In one embodiment, the cost metric associated with each branch of thesearch tree includes an estimated combined current draw of the VCMs.Referring to the example of FIGS. 3B and 3C, the execution ordercorresponding to path 30 through the first search tree and the executionorder corresponding to path 32 through the second search tree include acollision due to concurrently seeking both VCMs in order to access thedata tracks associated with command 1 of the first search tree andcommand 2 of the second search tree. Accordingly in one embodiment, thecombined current draw of both VCMs due to the concurrent seek may causean overcurrent condition, and therefore the cost metric associated withselecting path 30 and path 32 as the execution order for the VCMs isincreased. The cost metric may be increased in any suitable manner, suchas by adding a predetermined offset or by adding an offset that isproportional to an amplitude of the estimated combined current draw,proportional to a duration the amplitude exceeds a threshold, etc.

In many cases, the increased cost metric associated with two pathsthrough the search trees that include a collision means at least one ofthe paths will not be selected as the optimal execution order. That is,in many cases the smallest accumulated cost metric for the selectedpaths will not result in a collision between the two paths. In somecases, however, the minimum accumulated cost metric for the pathsthrough both search trees will include a collision. Referring again tothe above example, it may be that the path 30 through the first searchtree of FIG. 3B and the path 32 through the second search tree of FIG.3C may correspond to the minimum accumulated cost metric even thoughincreased due to the collision. In one embodiment, when the pathsselected through the search trees includes a collision, at least one ofthe seek profiles is modified in order to avoid the overcurrentcondition when concurrently seeking the VCMs. The seek profile may bemodified in any suitable manner to avoid the overcurrent condition, suchas by decreasing an acceleration current during an acceleration phase ofthe seek or decreasing a deceleration current during a decelerationphase of the seek.

FIG. 4A shows an example wherein a seek of the first VCM 16 ₁ may bebased on a normal seek profile 34 and corresponding driving current 36,and a seek of the second VCM 16 ₂ may be based on a de-rated seekprofile 38 and corresponding driving current 40. A de-rated seek profileachieves a just-in-time (JIT) seek wherein the head arrives at thetarget data track just before reaching the target data sector of theaccess command, thereby reducing the power consumption of the seek. Thatis when there is sufficient time for the head to reach a target datatrack, the seek profile may be de-rated so that the coast velocity isless than a maximum coast velocity, thereby reducing the power consumedduring the acceleration and deceleration phase of the seek. In theexample of FIG. 4A, the normal seek profile 34 of the first VCM 16 ₁ andthe de-rated seek profile 38 of the second VCM 16 ₂ may initiateconcurrently leading to an overcurrent condition due to the combinedcurrent draw during the acceleration phase of the seeks (a magnifiedview of the acceleration phase is shown in FIG. 4B). In order to avoidthe overcurrent condition, the control circuitry 22 adjusts the de-ratedseek profile 38 for the second VCM 16 ₂ to seek profile 42 withcorresponding driving current 44. In this embodiment, the de-rated seekprofile 38 is adjusted by decreasing the acceleration current applied tothe second VCM 16 ₂ for a clamp interval 46 as shown in FIG. 4B. Thisdecrease in acceleration during the clamp interval 46 avoids theovercurrent condition by decreasing the combined current draw of bothVCMs. In one embodiment, after the clamp interval 46 the controlcircuitry 22 increases the acceleration current applied to the secondVCM 16 ₂ (as shown in FIG. 4B) so that the second VCM 16 ₂ reaches themaximum coast velocity, thereby causing the second VCM to “catch up” thelost seek distance due to clamping the acceleration during the clampinterval 46. In one embodiment, the clamp interval 46 is configured bythe control circuitry 22 so that the head may decelerate along the sametrajectory of the de-rated, JIT seek profile 38. In this manner, thepower consumption of the adjusted seek profile 42 may be minimized whilemaintaining the same seek performance (seek time) as the de-rated, JITseek profile 38.

FIG. 5A shows an embodiment wherein the de-rated seek profile 38 of thesecond VCM 16 ₂ is modified to seek profile 48 with correspondingdriving current 50, wherein the acceleration phase of the modified seekprofile 48 is delayed by a delay interval 52 as shown in FIG. 5B. Inthis manner, delaying the acceleration phase of the seek profile 48avoids the driving currents 36 and 50 of the first and second VCMs fromoverlapping, thereby avoiding the overcurrent condition. In the exampleof FIG. 5A, the modified seek profile 48 causes the second VCM 16 ₂ toreach a maximum coast velocity in order to “catch up” the lost seekdistance due to delaying the acceleration phase, thereby enabling thehead to decelerate along the same trajectory of the de-rated, JIT seekprofile 38. In this manner, the power consumption of the adjusted seekprofile 48 may be minimized while maintaining the same seek performance(seek time) as the de-rated, JIT seek profile 38.

In one embodiment, the access commands received from the host may bequeued in a command queue and sorted into an optimal execution orderusing a rotational position optimization (RPO) algorithm. The RPOalgorithm may be adapted over time based on a measured seek time foreach seek operation (i.e., each seek length). That is, the estimatedseek times for each seek length in the RPO algorithm may be adjustedover time based on the actual seek times measured after each seekoperation. In one embodiment, when a seek profile is modified to avoidan overcurrent condition as described above, the measured seek time forthe seek may still be used to adapt the RPO algorithm. For example,delaying a seek profile as described above with reference to FIG. 5A maychange a de-rated seek profile into a normal seek profile that may stillbe a typical seek profile under other operating conditions. Thereforethe measured seek time for the seek operation may still be used to adaptthe RPO algorithm. FIG. 6A shows an embodiment wherein the decelerationphase of a normal seek profile 34 with corresponding driving current 36overlaps with the deceleration phase of a de-rated seek profile 54 withcorresponding driving current 56, thereby resulting in an overcurrentcondition during the deceleration phases of the seeks. In order to avoidthe overcurrent condition, the de-rated seek profile 54 is modified toseek profile 58 with corresponding driving current 60 which extends theacceleration interval during the acceleration phase by interval 62 asshown in FIG. 6B. Extending the acceleration interval causes the secondVCM 16 ₂ to reach a maximum coast velocity, thereby enabling thedeceleration phase of the modified seek profile 58 to begin earlier asshown in FIG. 6A so as to avoid the overlap in the deceleration drivingcurrents during the deceleration phase of the concurrent seeks.

In one embodiment when the seek profiles for both VCMs are normal seekprofiles (not de-rated or slightly de-rated), and both seek profilesterminate near the inner or outer diameter of the disk, the cost metricfor one of the seek profiles may be modified by adding a revolution oflatency to one of the seeks. That is, a normal seek profile may bemodified based on an additional revolution of latency, which in oneembodiment means the normal seek profile may be converted into ade-rated seek profile due to the increased seek time. If an overcurrentcondition still occurs due to concurrently seeking both VCMs (e.g.,during the acceleration phase of concurrent seeks), the de-rated seekprofile may be modified as described above in order to avoid theovercurrent condition.

Any suitable technique may be employed to estimate the current draw ofeither VCM during a seek operation. FIG. 7A shows an embodiment whereinfor each VCM a first peak current window W1 is estimated for theacceleration phase of a seek profile, and a second peak current windowW2 is estimated for the deceleration phase of the seek profile. Thecombined current draw for both actuators is then estimated based on anoverlap of the peak current windows. In one embodiment, there may be aseek time offset between the VCMs resulting in a partial overlap of thepeak current windows. For example, a seek of the first VCM 16 ₁ may beinitiated and then after a small delay a seek of the second VCM 16 ₂ maybe initiated. The amount of overlap between the peak current windows maythen be estimated by time shifting the peak current windows for thesecond VCM 16 ₂ before estimating the degree of overlap. When an overlapis detected, an overcurrent condition is assumed during the duration ofthe overlap. In one embodiment, the width of each peak current window W1or W2 may be calibrated and optionally tuned over time in order toensure an overlap of the windows accurately predicts an overcurrentcondition.

In one embodiment, a center of a peak current window W1 or W2 may shiftin time relative to the seek time for a given seek length. An example ofthis embodiment is shown in FIG. 7B wherein the center of each peakcurrent window W1 and W2 shifts in time relative the length of each seekoperation. In one embodiment, the shift of the peak current windows W1and W2 is calibrated by measuring the shift for different seek lengthsduring a calibration procedure, and then generating a suitable function(e.g., a polynomial) for estimating the window shift based on the seeklength. When sorting the access commands into an execution order basedon the search tree as described above, the combined current draw of theVCMs may be estimated by computing the center of the peak currentwindows W1 and W2 for each VCM based on the seek length of thecorresponding access command.

In one embodiment, when sorting the access commands into an optimalexecution order, there may be insufficient time to estimate the combinedcurrent draw of the VCMs for every access command in every path throughthe search tree, particularly as the depth of the search tree increases(length of the command queue increases). According in one embodiment,the access commands may be first sorted into a plurality of candidateexecution orders based on a cost metric that does not include theestimated combined current draw of the VCMs. An accumulated cost metricmay then be computed for each candidate execution order based on a costmetric that includes the estimated combined current draw of the VCMs asdescribed above, wherein the candidate execution order having thesmallest accumulated cost metric is then selected as the optimalexecution order.

An example of this embodiment is understood with reference to the flowdiagram of FIG. 8, wherein a plurality of access commands received froma host are stored in respective command queues for each VCM (block 64).When sorting the access commands into an execution order, a first costmetric is generated for each branch of a search tree as described above,wherein the first cost metric includes at least an access latencyassociated with executing an access command but does not include anestimated combined current draw of the VCMs (block 66). The accesscommands are then sorted into a plurality of candidate execution ordersbased on the first cost metric (block 68). For each candidate executionorder, a second cost metric is computed based on at least the estimatedcombined current draw of the VCMs (block 70), and one of the candidateexecution orders is selected as the optimal execution order based on thesecond cost metric (e.g., the candidate execution order having thesmallest accumulated cost metric). In one embodiment, the final costmetric for selecting the optimal execution order may be generated byadding the second cost metric to the first cost metric.

FIGS. 9A and 9B illustrate an example of this embodiment wherein theaccess commands of each command queue for each VCM are first processedusing a search tree based on a first cost metric that does not includethe estimated combined current draw of the VCMs. At least two candidateexecution orders (two paths) through each search tree are selected basedon the first cost metric. For example, a predetermined number ofexecution orders having the smallest accumulated first cost metric areselected as the candidate execution orders. In the example of FIG. 9A,candidate execution orders 76 and 78 are selected, and in the example ofFIG. 9B, candidate execution orders 80 and 82 are selected. A secondcost metric is then computed for the candidate execution orders whichtakes into account the estimated combined current draw of the VCMs asdescribed above. When a collision is detected due to the concurrent seekof the VCMs, the second cost metric may or may not change the candidateexecution order having the smallest accumulated cost metric as describedabove. Sorting the access commands into an optimal execution order byfirst generating candidate execution orders and then considering thecombined current draw of the VCMs reduces the execution time of the sortalgorithm.

In one embodiment, the data storage device may comprise more than twoactuators (e.g., more than two VCMs) wherein concurrently seeking two ormore of the actuators may result in an overcurrent condition.Accordingly the aspects in the embodiments described above may beextended to account for concurrently seeking more than two actuators,such as by modifying more than one seek profile in order to avoid anovercurrent condition.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a data storage controller, orcertain operations described above may be performed by a read channeland others by a data storage controller. In one embodiment, the readchannel and data storage controller are implemented as separateintegrated circuits, and in an alternative embodiment they arefabricated into a single integrated circuit or system on a chip (SOC).In addition, the control circuitry may include a suitable power largescale integrated (PLSI) circuit implemented as a separate integratedcircuit, integrated into the read channel or data storage controllercircuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In another embodiment, the instructions are stored on the diskand read into a volatile semiconductor memory when the disk drive ispowered on. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry. In someembodiments, at least some of the flow diagram blocks may be implementedusing analog circuitry (e.g., analog comparators, timers, etc.), and inother embodiments at least some of the blocks may be implemented usingdigital circuitry or a combination of analog/digital circuitry.

In various embodiments, a disk drive may include a magnetic disk drive,a hybrid disk drive comprising non-volatile semiconductor memory, etc.In addition, some embodiments may include electronic devices such ascomputing devices, data server devices, media content storage devices,etc. that comprise the storage media and/or control circuitry asdescribed above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device comprising: a first disksurface; a first head; a first actuator configured to actuate the firsthead over the first disk surface; a second disk surface; a second head;a second actuator configured to actuate the second head over the seconddisk surface; and control circuitry configured to: receive a pluralityof access commands from a host; compute a cost metric for executing aseek to execute each access command of the plurality of access commands,wherein the cost metric is based on an access latency of the seek, apower consumption of the seek, and an estimated combined current draw ofthe first and second actuators during the seek; and sort the accesscommands into an execution order based on the cost metrics computed forthe access commands.
 2. The data storage device as recited in claim 1,wherein the control circuitry is further configured to: estimate a peakcurrent window for the seek of each access command; and estimate thecombined current draw of both actuators based on an overlap of the peakcurrent windows.
 3. The data storage device as recited in claim 2,wherein the peak current window is estimated based on a length of theseek.
 4. The data storage device as recited in claim 2, wherein the peakcurrent window corresponds to at least one of an acceleration phase ofthe seek or a deceleration phase of the seek.
 5. The data storage deviceas recited in claim 1, wherein when the execution order results in aconcurrent seek of the first and second actuators, the control circuitryis further configured to modify a seek profile of at least the secondactuator.
 6. The data storage device as recited in claim 5, wherein thecontrol circuitry is further configured to modify the seek profile of atleast the second actuator by decreasing an acceleration current appliedto the second actuator for a clamp interval of an acceleration phase ofthe seek profile.
 7. The data storage device as recited in claim 6,wherein the control circuitry is further configured to modify the seekprofile of at least the second actuator by increasing the accelerationcurrent applied to the second actuator after the clamp interval.
 8. Thedata storage device as recited in claim 5, wherein the control circuitryis further configured to modify the seek profile of at least the secondactuator by delaying an acceleration phase of the seek profile.
 9. Thedata storage device as recited in claim 8, wherein the control circuitryis further configured to modify the seek profile of at least the secondactuator by increasing a constant velocity phase of the seek profile.10. A data storage device comprising: a first disk surface; a firsthead; a first actuator configured to actuate the first head over thefirst disk surface; a second disk surface; a second head; a secondactuator configured to actuate the second head over the second disksurface; and control circuitry configured to: receive a plurality ofaccess commands from a host; compute a first cost metric for executing aseek to execute each access command of the plurality of access commands,wherein the first cost metric is based on at least an access latency ofthe seek; sort the access commands into a plurality of candidateexecution orders based on the first cost metrics computed for the accesscommands; compute a second cost metric for executing a seek to executeeach access command in each of the candidate execution orders, whereinthe second cost metric is based on an at least an estimated combinedcurrent draw of the first and second actuators during the seek; selectone of the candidate execution orders based on the second cost metrics;and execute the access commands based on the selected execution order.11. The data storage device as recited in claim 10, wherein at least oneof the first cost metric or the second cost metric is further based on apower consumption of the seek.
 12. The data storage device as recited inclaim 10, wherein the control circuitry is further configured to:estimate a peak current window for the seek of each access command; andestimate the combined peak current of both actuators based on an overlapof the peak current windows.
 13. The data storage device as recited inclaim 12, wherein the peak current window is estimated based on a lengthof the seek.
 14. The data storage device as recited in claim 12, whereinthe peak current window corresponds to at least one of an accelerationphase of the seek or a deceleration phase of the seek.
 15. The datastorage device as recited in claim 10, wherein when the selectedexecution order results in a concurrent seek of the first and secondactuators, the control circuitry is further configured to modify a seekprofile of at least the second actuator.
 16. The data storage device asrecited in claim 15, wherein the control circuitry is further configuredto modify the seek profile of at least the second actuator by decreasingan acceleration current applied to the second actuator for a clampinterval of an acceleration phase of the seek profile.
 17. The datastorage device as recited in claim 16, wherein the control circuitry isfurther configured to modify the seek profile of at least the secondactuator by increasing the acceleration current applied to the secondactuator after the clamp interval.
 18. The data storage device asrecited in claim 15, wherein the control circuitry is further configuredto modify the seek profile of at least the second actuator by delayingan acceleration phase of the seek profile.
 19. The data storage deviceas recited in claim 18, wherein the control circuitry is furtherconfigured to modify the seek profile of at least the second actuator byincreasing a constant velocity phase of the seek profile.
 20. A datastorage device comprising: a first disk surface; a first head; a firstactuator configured to actuate the first head over the first disksurface; a second disk surface; a second head; a second actuatorconfigured to actuate the second head over the second disk surface; ameans for receiving a plurality of access commands from a host; a meansfor computing a cost metric for executing a seek to execute each accesscommand of the plurality of access commands, wherein the cost metric isbased on an access latency of the seek, a power consumption of the seek,and an estimated combined current draw of the first and second actuatorsduring the seek; and a means for sorting the access commands into anexecution order based on the cost metrics computed for the accesscommands.